The present invention relates to a molded rubber material for golf balls, which is used as a constituent of a golf ball. Particularly, the present invention relates to a spherical molded rubber material to be used as the core of solid golf balls, such as two-piece or three-piece golf balls. More particularly, the present invention relates to a high-quality hard molded rubber material for golf balls, a method for producing the molded rubber material efficiently, and a golf ball.
A solid golf ball has a core which accounts for its major portion; therefore, it depends largely on its core for its quality. Consequently, attempts have been made to develop a new core with higher hardness and better hardness distribution, which impart improved rebound resilience to golf balls. In other words, there is a demand for a molded rubber material for golf balls with high rebound resilience.
For the development of golf balls with high rebound resilience, there have been proposed several technologies of incorporating a rubber compound with an organic sulfur compound in an adequate amount. These technologies improve the rebound resilience of the core but take a longer time for vulcanization (or reaction), with the productivity of cores decreasing.
Incorporation with a vulcanization accelerator is a common practice for accelerating the reaction of rubber with a vulcanizing agent, as disclosed in the following patents.
U.S. Pat. No. 6,878,075
U.S. Pat. No. 6,767,940
U.S. Pat. No. 6,695,718
Unfortunately, incorporation of a vulcanization accelerator into a rubber compound adversely affects the rebound resilience of molded material. Thus, there is a demand for a core material which can be vulcanized efficiently without any adverse effect on rebound resilience.